弯曲河流裁弯后牛轭湖进口淤积模型

根据2011—2017年黄河源野外调查，发现若尔盖黑河流域牛轭湖进口段以推移质淤积为主，但是其淤积过程与主控因素却不明晰。通过分析裁弯后牛轭湖进口段的推移质淤积过程及其影响因素，构建相应的简化物理图形，建立其进口段推移质淤积过程的理论模型，并采用野外观测数据验证。数值计算表明，进口段的淤积速率是上游来沙量、沙栓长度和原河道分流角的函数，即沙栓越短、上游来沙量越大和分流角越大，牛轭湖进口淤积完成所需时间越短。概化模型用于模拟黑河上游麦曲的某个牛轭湖进口段淤积过程，其计算值与实测值较符合，但也存在一定误差，主要因为该牛轭湖形成后经历了2013—2016年的洪水期，其来流量与输沙量是非恒定，且存在较大变幅。

Conceptual model of deposition process in oxbow lake inlet on a small meandering river

From the 2011-2017 field surveys of the Yellow River source region, bedload deposition was found to be the leading pattern in the inlet section of an oxbow lake on the Black River of the Zoige basin, but the deposition process and its control factors remain unclear yet. This paper gives a theoretical analysis to clarify this issue, draws a sketch of its relevant physics, and constructs a conceptual model of deposition process. This model is used in the numerical calculations and verified against survey data. Numerical results show that the deposition rate at the inlet section is a function of its upstream sediment supply, the length of its sand plug, and the diversion angle between the new and old channels, and that the time span of the inlet deposition stage is shorter in the case of a shorter plug, more supply, or larger angle. Application of the model to the simulations of deposition and formation of another oxbow lake in the upper Black River achieves a good agreement with measurements. It also reveals a modeling error in the lake formation during the four flood seasons of 2013-2016 and its causes ? unsteady incoming flow and sediment and their large variation ranges.